How Do I Make My Own Silicone Molds?

Silicone mold making allows you to create custom molds for a variety of projects. Silicone molds are flexible and durable, making them reusable. Creating your own silicone molds gives you more control over the mold shape and size for your specific needs.

Making your own molds has several advantages over buying premade molds:

You can create molds in the exact shape and size you need for your project.
Custom molds often cost less than buying specialized premade molds.
Silicone molds can be reused repeatedly, saving money in the long run.
You can quickly and easily make new molds if your project needs change.

Overall, making your own silicone molds gives you more flexibility, customization options, and potential cost savings compared to purchasing commercial molds.

Table of Contents

Materials Needed

The key materials needed to make silicone molds are:

Silicone rubber – This is the main material that will be poured into the mold frame to create the flexible mold. Common choices include platinum-cure silicone, tin-cure silicone, and condensation-cure silicone. Each has different properties in terms of cure time, tear strength, and Shore hardness. Platinum-cure silicone such as Smooth-Sil 940 is popular for its convenience and quality.

Mold frame/box – This contains the liquid silicone as it cures. The frame should be leakproof and made from a non-stick material such as plastic, resin, fiberglass, wood, or metal. The mold subject should be anchored to the base of the frame. Popular options include LEGO-style mold boxes and dam & putty edges.

Release agent – This lubricant allows the cured silicone to be detached from the mold frame and model surface. Common release agents include petroleum jelly, liquid soap, glycerin, and specialty silicone release sprays such as Universal Mold Release.

Safety Precautions

When working with liquid silicone to create molds, there are some important safety precautions to take:

Ventilation – Work in a well-ventilated area to avoid breathing in fumes from the silicone. Open windows and use fans to circulate fresh air. If working indoors, consider wearing a respirator mask rated for organic vapors. Improper ventilation when working with liquid silicone can cause dizziness, headaches, and nausea (Source).

Avoid skin contact – Wear nitrile gloves when handling liquid silicone to prevent skin irritation. The chemicals in uncured silicone can cause rashes or eczema with repeated exposure (Source). Cover exposed skin and wear eye protection. Wash hands thoroughly after working with silicone.

Making the Mold Box

When making a silicone mold, you’ll need to construct a mold box to contain the liquid silicone as it cures. The box needs to be watertight to prevent leaks. There are a few considerations when selecting materials and designing the mold box:

For the box material, opt for a rigid material like wood, PVC plastic, acrylic sheets, or cardboard. Avoid porous materials like paper or foam which could absorb silicone. Plastic containers like food storage containers also work well. Make sure the walls are thick and sturdy enough to withstand the pressure of liquid silicone.

To seal the box, use a non-porous tape like masking tape, duct tape, or packing tape. For a more permanent seal, you can use silicone caulk or glue. Apply the sealant generously along the interior seams and corners to prevent leaks.

When designing the box, make sure it is large enough to fully contain your mold with at least 1-2 inches of clearance on all sides. The box should have an open top to pour silicone into. You can include registration keys – plastic pieces extending from the sides – to ensure the two halves align properly. An optional lid can help protect the mold when not in use.

For more details, refer to this guide on constructing a silicone mold box: How To Build A Box For Mold Making

Preparing the Silicone

Properly preparing the silicone is a crucial step to ensure your finished mold will have minimal bubbles and defects. Here are some tips for mixing and degassing your silicone rubber:

Follow the manufacturer’s instructions closely for mix ratios and mixing times. Typically two parts of silicone base are combined with one part of a catalyst. Thoroughly stir the two parts together, scraping the sides and bottom of the container to incorporate all material. Mix for the recommended time, usually 2-3 minutes. Mix too short and the silicone may not properly cure; too long and bubbles can get whipped into the mixture.

Next, the mixed silicone should be degassed. This removes any air bubbles introduced during mixing. There are several degassing options:

A vacuum degassing chamber – Pulls a vacuum on the silicone to draw out bubbles.
A pressure pot – Forces air bubbles to compress under pressure.
Letting the silicone sit – Bubbles will slowly rise to the surface over 30+ minutes.

Vacuum chambers provide the best results for commercial productions. For hobby or small projects, letting the silicone self-degas in a container is often sufficient. The goal is to remove as many bubbles as possible before pouring the mold.

Once mixed and degassed, the silicone is ready to be carefully poured into the mold box. Work slowly and avoid creating new bubbles in the liquid silicone rubber. Tap the mold box occasionally as you pour to help dislodge any stubborn bubbles.

Pouring the Silicone

Once the silicone components have been thoroughly blended together, it’s time to pour the silicone into the mold box. When pouring the silicone, it’s important to coat all surfaces of the mold box evenly and fill in any hard-to-reach areas first. According to Silicone Mold Making – Three Different Ways, pour the silicone in a thin stream along the edges of the mold box, allowing it to slowly cover the bottom and sides.

Pour carefully and slowly to prevent creating bubbles in the silicone. If any bubbles form on the surface, use a toothpick or skewer to pop them. Pour until the silicone covers the object by at least 1/2 inch on all sides. As noted in How to Make A Silicone Mold, overfilling is better than underfilling to ensure full mold coverage.

Once poured, do not disturb or move the silicone. Allow it to fully cure according to the manufacturer’s instructions, which can take 16-24 hours. The silicone will change color slightly when fully cured. When cured, the flexible silicone mold can be easily unmolded and is ready for casting resin, wax, soap, or other materials.

Unmolding

Carefully removing your silicone molds is crucial to getting cleanly shaped items. Silicone naturally has some stickiness, so you’ll need to use a release agent. There are two main options:

Flour/cornstarch – Dust a thin layer over the interior of the mold before pouring your material. Tap gently to remove excess.

Baking spray – According to Rose Levy Beranbaum, products like Baker’s Joy work well since they contain both oil and flour. Spray a light coating before pouring.

When unmolding, gently flex the sides and corners of the mold to release suction. Don’t pull too hard or you may deform the molded item. Unmold over a sheet of parchment to catch any crumbs or spills.

Using the Mold

Once your silicone mold has fully cured, it’s ready for casting. Properly preparing the mold surface and selecting the right casting material are key steps for getting the best results.

Before casting, make sure the mold surface is clean and free of debris. Any remaining mold release or particles could negatively impact your cast. Gently wash the mold with warm soapy water and allow to fully dry. You may also want to apply a thin layer of mold release to help prevent the casting material from sticking.

When selecting your casting material, consider factors like cure time, viscosity, and demold time. For example, a low viscosity resin will pick up greater detail from the mold compared to a thicker silicone or rubber. The cure and demold times need to match the complexity of the mold shape – longer cure times are better for deep undercuts. Test different materials to find what works best with your particular mold design.[https://formlabs.com/blog/how-to-make-silicone-molds/]

Mold Maintenance

Proper cleaning and storage of your silicone molds is important for maximizing their longevity. It’s recommended to wash molds with warm water and a small amount of dish soap after each use. Gently scrub the mold clean, taking care not to damage the surface. Rinse thoroughly to remove any soap residue. Allow the mold to air dry completely before storing, as moisture can encourage mold growth. According to this source, you don’t need any special cleaners for silicone molds – simple soap and water will do the trick.

Store cleaned molds in a dry, dust-free space at room temperature out of direct sunlight. Exposure to light and heat can degrade the silicone over time. Avoid storing molds in plastic bags or containers, as trapped moisture causes mold growth. Before re-using a stored mold, check it over closely for any tears or damage.

If your silicone mold becomes damaged, small tears can often be repaired. Thoroughly clean and dry the area to be patched. Apply a small amount of clear silicone sealant to the damaged area, smoothing it flush with the surrounding surface. Allow several hours for the sealant to fully cure before using the mold again. Severely damaged molds with large tears or holes may need to be replaced.

Advanced Techniques

Once you have mastered the basics of silicone mold making, you can move on to more advanced techniques to create more complex molds. Here are some of the most common advanced techniques used:

Multi-Part Molds

For intricate objects or shapes with undercuts, you may need to create a multi-part mold. This involves creating a mold box with mold walls that can be separated after the silicone cures. The mold can then be carefully pulled apart to remove the original object. Common techniques for multi-part molds include a two-sided mold or a mold with mold jacket walls.

Adding Color

You can add pigments to your silicone to create colored molds. Smooth-On makes a variety of SO Strong pigments that can be combined with platinum or tin cure silicones. Adding pigments allows you to create visually appealing molded pieces.

Embedding Objects

You can embed various objects in your silicone mold to create texture or add design elements. Some common items embedded include fabrics, beads, stones, or metal mesh. Make sure any items are compatible with your silicone and will not inhibit curing. Place the objects carefully before pouring the silicone to hold them in place.